They can be inserted in-line just after the connection to the 30 or 47 ltr tanks. Allowing you to turn off the water supply if you need to undertake any maintenance. They can also be added to the end of a layout so that now and again you can open the tap and allow the lines to be flushed, removing a sediment or lime scale build-up that might occur over time. This will only take a couple of minutes and only needs to be done every couple of weeks.
Please note that this product is sold individually.